Currently, the transition to a renewable energy society is an important issue that is common to developed countries. In response to this issue, there has been a demand for construction for a technology base using hydrogen (H2) as an energy source.
Hydrogen is considered as a first candidate for clean secondary energy. However, since hydrogen itself is difficult to liquefy, a liquid carrier from which hydrogen can be generated and which is easy to store and transport has been desired.
Among the examples, from the viewpoint that the hydrogen density is high and liquefaction is easily carried out (liquefaction conditions: less than 1 MPa, room temperature), ammonia (NH3) is considered as a promising liquid carrier.
Since NH3 is free from carbon, NH3 has been attracting attention as an alternative fuel for petroleum or the like. From the viewpoint that the octane value is high and the compression ratio can be increased, NH3 can be applied to a substantially compact and fuel-efficient combustor.
Hereinafter, a reaction formula related to NH3 combustion (exothermic reaction) is shown.NH3+3/4O2→1/2N2+3/2H2O ΔH°=−317 kJ/mol
As shown in the formula above, NH3 is a combustible gas and there is a possibility that NH3 can be widely utilized in internal combustion and external combustion engines such as automobiles, aircrafts, thermal power plants, and iron works as an alternative fuel for gasoline or light oil. However, in NH3 combustion, there is a problem in that nitrogen (N2) is generated and the generation of nitrogen is accompanied by generation of NOx.
In consideration of such problem, for example, PTL 1 suggests a catalyst for selective oxidative decomposition of ammonia in which an oxide of a first group metal and an oxide of a second group metal are supported by the surface of a ceramic catalyst carrier.
Further, PTL 2 suggests that an ammonia combustion catalyst contains at least one metal element selected from manganese-cerium oxides as catalyst A components and non-noble metal elements belonging to the groups 8 to 11 in the periodic table as catalyst B components.